preferred way of drilling through cabin walls or topside

[paulga]

I read an article on marinehowto that was recommended earlier here by other boaters. I may have got some points, but not all. I have tried to make a summary of things required based on my understanding, it would be great if you could point out what I have missed.


1. West system epoxy: #205 hardener #105 resin & thickener: Colloidal Silica, pump & syringe, toothpick for removing air bubble
2. dremel with magic wand (I'm not sure if this is needed for installing a cable seal). The cable seal is for an ethernet cable.
3. dremel bits #115 #654 (not sure if they are required for installing above cable seal). which one is a "countersink bit", #115 or the brad point bit, or a countersink drill bit?
4. Drill and bits: Brad Point Drill bit, countersink bit
5. shop vac
6. Gorilla Tape for injecting epoxy

For cable seals, the center hole is for the ethernet cable, the other holes are for screws. is the countersinking still preferred? is countersinking a screw hole different from countersinking a stanchion bolt hole that was covered in the article?

 

[Comodave]

Any time I am going to drill a hole through fiberglass I countersink the hole. If I am through bolting I use the countersink to make an O ring out of the caulk around the bolt. If I am screwing to fiberglass I use the countersink to make the O ring out of caulk but also to help prevent the gel coat from chipping when the screw threads bite into the glass. If you don’t countersink the gel coat may lift around the screw, sometimes very badly. Then you have a tough repair to do. Make the countersink just a bit wider than the screw threads. Also if you are screwing into fiberglass do not nake the drilled hole too small since the screw can bind in the hole and possibly break off. Glass isn’t like wood when screwing into it, wood will give if the pilot hole is too small fiberglass will not give.

 

[DDW]

I product that will make the job a little less messy (if you are filling the core with epoxy) is West Six10. This is the stuff in the caulking tube. It does cost more. The advantage is that it is pre-thickened the correct amount, mixes itself on the way out of the tube, and will not run out of a vertical or even overhead hole. It is very slow setting which can be an advantage or not, depending. You end up with a disposable nozzle (which must be disposed of) but no sloppy cups, sticks, syringes, etc.

 

[Flatswing]

Paul: from your post, it’s not clear whether you are drilling though a cored deck or solid. If solid, Commodave has summarized it nicely. definitely follow his chamfering advice to prevent gelcoat chipping and promote a nice seal around the fasteners.
If a cored deck, then the principle is to remove some core peripherally and seal this with thickened epoxy, so that your fitting (& fasteners) pass through a “solid” FRP tunnel. An easy way to do this is with the Keyhole bits referenced on Rod’s website. For small screw holes, it’s easier just to overdrill the screw holes by 3/32 more than outside diameter of fasteners, fill with thickened epoxy, then redrill for your screws. If you use this technique for self tapping screws rather than tapping for machine screws, know that you will need a much larger drill for screw holes than you are accustomed to. If you can’t turn the screw in by hand, the pilot hole is too small. If the pilot hole is too small, the screw will crack the nice epoxy tunnel you just created, and the core seal may be lost.
Bedit Butyl tape - sold by Rod Collins/ Marine history now on Amazon, is excellent alternative for this application if you don’t love caulk (just say no to 5200) both under the gland, around the cable and around the screws.

 

[paulga]

Paul: from your post, it’s not clear whether you are drilling though a cored deck or solid. If solid, Commodave has summarized it nicely. definitely follow his chamfering advice to prevent gelcoat chipping and promote a nice seal around the fasteners.
If a cored deck, then the principle is to remove some core peripherally and seal this with thickened epoxy, so that your fitting (& fasteners) pass through a “solid” FRP tunnel. An easy way to do this is with the Keyhole bits referenced on Rod’s website. For small screw holes, it’s easier just to overdrill the screw holes by 3/32 more than outside diameter of fasteners, fill with thickened epoxy, then redrill for your screws. If you use this technique for self tapping screws rather than tapping for machine screws, know that you will need a much larger drill for screw holes than you are accustomed to. If you can’t turn the screw in by hand, the pilot hole is too small. If the pilot hole is too small, the screw will crack the nice epoxy tunnel you just created, and the core seal may be lost.
Bedit Butyl tape - sold by Rod Collins/ Marine history now on Amazon, is excellent alternative for this application if you don’t love caulk (just say no to 5200) both under the gland, around the cable and around the screws.

It's the salon wall inside the sundeck. How to tell it is cored or solid ?
Cored = the sandwich is balsa or foam?
Solid = the sandwich is plywood?

 

[rslifkin]

It's the salon wall inside the sundeck. How to tell it is cored or solid ?
Cored = the sandwich is balsa or foam?
Solid = the sandwich is plywood?

Any kind of sandwich is cored. Solid would be if it's just fiberglass with no sandwich. You may be able to get a good idea by tapping on it and listening to the difference in sound between different parts of the boat, but unless you know ahead of time what that part of the boat is made of, you may not be 100% sure until you start drilling and see what you drill through.


Personally, I like to drill through a piece of painter's tape and also run the drill bit or hole saw backwards at first to wear through the gelcoat before reversing direction and drilling the rest of the way through. The combination of the 2 methods generally avoids chipping the gelcoat around the hole.

 

[paulga]

Any kind of sandwich is cored. Solid would be if it's just fiberglass with no sandwich. You may be able to get a good idea by tapping on it and listening to the difference in sound between different parts of the boat, but unless you know ahead of time what that part of the boat is made of, you may not be 100% sure until you start drilling and see what you drill through.


Personally, I like to drill through a piece of painter's tape and also run the drill bit or hole saw backwards at first to wear through the gelcoat before reversing direction and drilling the rest of the way through. The combination of the 2 methods generally avoids chipping the gelcoat around the hole.

If it is cored fibreglass, and the screw dia is 1/4", then use a 1/4"+3/32" =11/32" brad point bit to drill, correct?

 

[Circumnavigator]

I agree with putting a piece of tape over the spot before drilling, but also, if drilling through, I like to drill a very small hole through and then drill out to size halfway from each side. That way you avoid chipping the gel coat on the other side.


Jim

 

[jbinbi]

Is this to put a cable clam in to lead the enet cable from outside to inside?

If so, the hole for the cable doesn't need to be countersunk though it will be nicer if you do. I would countersink the screw holes that are used to hold the clam to the fiberglass. You don't need any epoxy if this is what you are doing. They make countersink kits for 8/10/12 etc. screws

 

[paulga]

Is this to put a cable clam in to lead the enet cable from outside to inside?

If so, the hole for the cable doesn't need to be countersunk though it will be nicer if you do. I would countersink the screw holes that are used to hold the clam to the fiberglass. You don't need any epoxy if this is what you are doing. They make countersink kits for 8/10/12 etc. screws

I didn't get exactly what is the countersink method in Rod's article?

 

[Flatswing]

I didn't get exactly what is the countersink method in Rod's article?

Perhaps it might be clearer to think of slightly ( not deeply) chamfering the edge of the hole in the outer FRP skin. This forms a small “well” that will hold the sealant/ butyl tape ensuring a nice seal around the shank of the fastener and the underside of the fitting (in this case the cable gland) as the fastener is tightened.

Perhaps I’m wrong , but I think of countersinking as burying the head of the fastener flush or slightly below the surface. Perhaps semantics but most often I find the head of the fastener is either an oval head seated inside a finishing washer, or flat head seated in the fitting. Other than wood, where I’m covering the countersunk screw with a teak plug, I can’t recall countersinking fasteners into FRP on board.